PROJECT SUMMARY Research: Therapeutic resistance limits the efficacy of anti-PD-1 therapy for cancer: only 40% of melanoma patients respond to this therapy, and half of these will develop resistance. Resistance can arise from several mechanisms including mutations acquired by cancer cells or infiltration of tumors by immunosuppressive immune cells. There is a critical need to understand resistance mechanisms to develop novel immunotherapeutic strategies to overcome them. Based on our preliminary data, we hypothesize that cancer cells with resistance mutations recruit unique immunosuppressive myeloid populations that can be targeted to overcome resistance to anti-PD-1. To test this hypothesis, in Aim 1 we will determine how clinically-defined resistance mutations impact immunosuppressive myeloid populations in mouse models using single-cell RNA-sequencing and in human melanoma biopsies using multiplex immunofluorescence. In Aim 2 we will determine how inhibition of myeloid cells can overcome resistance to anti-PD-1 with mechanistic mouse studies. This research will define how to personalize immunotherapy based on a patient?s unique cancer mutations and infiltrating immunosuppressive myeloid cells, with the long-term goal to improve responses to immunotherapy. Candidate and Mentorship: The PI, Brian Miller, MD PhD, is an oncologist and cancer immunologist at the Dana-Farber Cancer Institute and Harvard Medical School. He spends 90% of his time in translational research and 10% in clinical practice caring for patients with cancer. His goal is to lead an independent academic research laboratory studying the functions of myeloid cells in the tumor microenvironment and developing therapeutic strategies to overcome resistance to immunotherapy. He will pursue this goal by: 1) developing expertise in the generation and analysis of single-cell RNA-sequencing data; 2) becoming an expert in myeloid cell biology and developing in vitro and in vivo functional assays; 3) establishing a community of mentors and collaborators; 4) completing coursework to expand his computational and statistical background. He will be mentored by Dr. Arlene Sharpe, an expert in tumor immunology, along with a strong scientific advisory committee with expertise in computational biology, myeloid cells, and translational immunotherapy: Dr. Peter Kharchenko, Dr. Jon Kagan, and Dr. Stephen Hodi. These mentors and his career development plan will help him acquire the skills and expertise needed to develop his own distinct niche in single-cell analysis of the tumor microenvironment and functional dissection of tumor-infiltrating myeloid cells. Environment: Dr. Miller will conduct this research at Harvard Medical School and leverage the exceptional research and teaching environment at Harvard, the Dana-Farber Cancer Institute, and the Broad Institute. In addition, his network of collaborators at the Dana-Farber Cancer Institute, Broad Institute, and Bristol-Myers Squibb will provide reagents, technical assistance, and expertise to ensure his success. Dr. Miller has access to the necessary tools to successfully complete his proposed research and transition to independence.